There is an extensive body of literature on hydrophilic monomers in the art and a large number of such monomers are commercially available. These monomers impart hydrophilicity, water absorption, and/or improve the wetting properties of materials having them copolymerized therein over the same material absent such monomers. They also result in highly hydrophilic, highly absorbent, and highly wettable homopolymeric materials. These commercial monomers can be obtained from typical monomeric suppliers such as ROHM Tech, typically under the MHOROMER.RTM.D series; Sartomer; and Alcolac, typically under the SIPOMER.RTM. series.
A general characteristic of such known modifiers is that there is a hydrophilic group and a copolymerizable group. A typical example is N-vinyl pyrrolidone; another is hydroxyethylmethacrylate. Each of these is suitable for copolymerizing with other monomers or oligomers containing one or more free (meth)acrylic or vinylic groups. The addition of the free hydroxy or the amide increases the hydrophilicity, water absorbability and wettability of the resulting polymers over those not having such monomers present.
For many utilities, it is desired that the polymeric materials resulting therefrom be in molded form. This is typical in the field of contact lenses. Also frequently, molds are poly(methyl methacrylate) and copolymerizing (a) the aforementioned modifying monomers with (b) the monomers or oligomers being modified in such molds results in etching and scarring of the molds. This is extremely disadvantageous for ultimate polymer utilities which require mar free surfaces, i.e. high quality optical surfaces. In these situations, molds must be replaced extremely frequently resulting in high production costs and slowed production rates.